Many thermostatic switches are known which have contacts mounted on flexible strips with at least one of the flexible strips being formed of or biased by a bimetal material for movement subject to temperature variations. With such constructions, it is possible to provide relatively accurate electrical control responsive to temperature changes.
In U.S. Pat. No. 3,223,809 to Wehl, a thermostatic switch is disclosed which includes a stacking insulator block for stack-assembling a thermostatic switch. Generally, first and second contact strips are disposed within a recess in the stacking block and placed within a housing. An insulative separator is disposed between the two contact strips. The separator is shaped for retention in the stacking block, and may be either T- or I-shaped, having a central portion sized for placement in the stacking block recess, with extending end portions for limiting separator movement.
The insulative separator is generally composed of a ceramic powder which is shaped and then heated, with the separator typically being made of porcelain. Such a material is non-conducting and insensitive to temperature variations, but is subject to cracking under stress.
In forming the separator, it is difficult to achieve sharp edges on the inner corners of the T- or I-shaped ceramic insulator, due to the small size of the separator and the shrinkage properties of the ceramic material. If excess material is present in the corners, the inner corners of the ceramic separator may contact the edges of the stacking block, causing a stress concentration. Thus, the separator may crack, resulting in short-circuiting and switch failure. Consequently, the separators are typically produced with a narrowed center portion to assure that the inner corners clear the edges of the stacking block with a large safety margin. However, this narrowing weakens the central portion and causes the separator to float within the stack, which may also result in cracking with switch failure.